title: Allosteric regulation of SERCA by phosphorylation-mediated conformational shift of phospholamban.
abstract: The membrane protein complex between the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) and phospholamban (PLN) controls Ca(2+) transport in cardiomyocytes, thereby modulating cardiac contractility. β-Adrenergic-stimulated phosphorylation of PLN at Ser-16 enhances SERCA activity via an unknown mechanism. Using solid-state nuclear magnetic resonance spectroscopy, we mapped the physical interactions between SERCA and both unphosphorylated and phosphorylated PLN in membrane bilayers. We found that the allosteric regulation of SERCA depends on the conformational equilibrium of PLN, whose cytoplasmic regulatory domain interconverts between three different states: a ground T state (helical and membrane associated), an excited R state (unfolded and membrane detached), and a B state (extended and enzyme-bound), which is noninhibitory. Phosphorylation at Ser-16 of PLN shifts the populations toward the B state, increasing SERCA activity. We conclude that PLN's conformational equilibrium is central to maintain SERCA's apparent Ca(2+) affinity within a physiological window. This model represents a paradigm shift in our understanding of SERCA regulation by posttranslational phosphorylation and suggests strategies for designing innovative therapeutic approaches to enhance cardiac muscle contractility.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics and Department of Chemistry, University of Minnesota, Minneapolis, MN 55455.
authors.forename: Martin
authors.initials: M
authors.lastname: Gustavsson
authors.forename: Raffaello
authors.initials: R
authors.lastname: Verardi
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Mullen
authors.forename: Kaustubh R
authors.initials: KR
authors.lastname: Mote
authors.forename: Nathaniel J
authors.initials: NJ
authors.lastname: Traaseth
authors.forename: T
authors.initials: T
authors.lastname: Gopinath
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Veglia
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping / Q000379:methods*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011817:Rabbits; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D008051:Lipid Bilayers; D008563:Membrane Lipids; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban
keywords: magic angle spinning; paramagnetic relaxation enhancement; protein-protein interactions; solid-state NMR